This invention relates to flying spot optical scanning systems and, more particularly, to optical scanning systems having multi-faceted rotating polygon beam scanning elements.
Multi-faceted rotating polygon beam scanning elements are commonly utilized in flying spot optical scanning systems. For example, they are frequently employed in raster input and output scanners for cyclically scanning an unmodulated or a modulated light beam through a predetermined scan angle in a line scanning direction.
As a general rule, a polygonal scanning element is rotated at an essentially constant angular velocity so that its facets sequentially intercept and reflect an input light beam. To avoid unwanted vignetting of the reflected light beam, provision is conventionally made for preventing the illumination of the active scanning facet from varying as a function of the rotation of the scanning element. To that end, some multi-faceted rotating polygon beam scanners are operated in a so-called overfilled mode in which two or more of the facets are simultaneously illuminated by the input beam. See, for example, U.S. Pat. No. 3,995,110. While overfilled scanners have been used with substantial success, such as in the commercially available 9700 electronic printing system of Xerox Corporation, they suffer from the disadvantage that a substantial part (i.e. 50% or more) of the available optical energy is wasted due to the inherent truncation of the input beam. Thus, others have suggested that such scanners be operated in fully filled mode or underfilled mode to avoid truncating the input beam. However, fully filled systems have tended to be relatively complex because they generally require facet tracking to maintain the input beam fully seated on the scanning facet while the reflected beam is being scanned through a desired scan angle. Underfilled systems, on the other hand, have traditionally been rather bulky and non-linear. See, for example, U.S. Pat. Nos. 3,675,016 and 3,750,189.